Sauna systems throughout history have employed various methods of heating a space to provide the therapeutic and cleansing effects of heat. As is well known, heat causes the human body to perspire and can also provide soothing and therapeutic effects to muscles and joints. Methods of heating a sauna include using open fires, enclosed stoves, and steam generators among others. While some forms of heat generation are effective to varying degrees, they can also present drawbacks. For example, the open fires found in old forms of Scandinavian saunas provided direct open flame heating, but also created intensely smoky rooms with short lived heat. Wood stoves enable a more controlled heat over a greater period of time, but also shield the heat due to the enclosed nature of the stove.
Saunas using electrically energized radiant heaters have also been developed. These systems employ infrared heating panels to generate electromagnetic radiation within the infrared spectrum. When absorbed by the body of a sauna user, the infrared radiation excites the molecules within the body to generate warming. Whereas steam or warm air generally only heat the skin and tissue directly beneath by conduction, infrared radiation more deeply penetrates the body (e.g., to about 1.5 inches) to more effectively and comfortably warm the body to a sweating temperature without the use of a conductive medium.
Radiant infrared heating systems are generally powered by conventional alternating current (AC) power sources, such as 110 volt, 60 Hz AC in the United States or 230 volt, 50 Hz AC in Europe. Such heating systems thus tend to generate some amount of low frequency (e.g., 50-60 Hz) electromagnetic (EM) radiation in addition to the desired infrared radiation utilized for heating. It has been estimated that in some cases infrared sauna systems may generate low frequency EM radiation with magnetic field levels as high as 60 milligauss. In comparison, areas under high voltage transmission lines have been measured with low frequency magnetic field levels as high as 1.9 milligauss and outdoor areas in open spaces have been measured with low frequency magnetic field levels as low as 0.3 milligauss.
Concerns about high levels of low frequency radiation have led to multiple methods for reducing the level of low frequency EM radiation in infrared heating systems. These include increasing the distance from the emitting source, reducing the exposure time to the radiation level and/or increasing shielding between the human body and the emitting source. Unfortunately, these methods are inherently limited for many sauna designs. For example, often exposure times cannot be controlled, or it may be impractical to reduce exposure time while also increasing distance between the human body and the emitting source. In addition, it may be difficult to increase distance given the normally confined nature of a sauna. Shielding the emitting source may undesirably reduce the effectiveness of the source, requiring longer exposure times and/or shorter distances to achieve similar effects. In addition, attempts have also been made to reduce the level of low frequency EM radiation through EM cancellation schemes, such as by producing multiple low frequency EM fields that tend to cancel one another.